The retina is a thin layer of neural tissue lining the back of the eye responsible for sensing visual stimuli. During development, the retinal vasculature is initiated by endothelial sprouts that lay down the primary arteries and veins that project outward radially from the optic disc to the retinal periphery, with a pair of capillary beds located on either side of the central layer of neurons further penetrating the retina. Patterning of the retinal vasculature is controlled by guidance cues driven initially by tissue hypoxia, which induces a vascular endothelial growth factor (VEGF) gradient sensed by tip cells, specialized endothelial cells at the front end of the growing vasculature. Tip cells migrate along a preexisting astrocyte network with endothelial stalk cells following the tip cells. Once in place, the primary vasculature undergoes maturation to specify arteries and veins, the nascent network is pruned, and the blood-retina barrier is formed. Recruitment of vascular smooth muscle cells and pericytes (also known as mural cells, contractile cells that wrap around endothelial cells of capillaries) aid in stabilization of the newly formed vessels. The molecular mechanisms controlling vessel development in the eye are not well understood.
In humans, retinal vascular development is usually accomplished around term birth but is delayed or arrested in retinal developmental disorders such as familial exudative vitreoretinopthy (FEVR). FEVR is characterized by hypovascularization of the retina due to the failure of peripheral retinal vascularization, followed by secondary aberrant neovascularization. Severe forms of FEVR present with bilateral congenital retinal folds or retinal detachment (FIG. 1). Currently, management of FEVR is by laser and surgery. While interventions improve the chance of retaining vision, more than 75% of eyes remain legally blind despite current best efforts. One study described improvement of retinal hemorrhage and neovascularization after ocular injection with bevacizumab (Avastin, a monoclonal antibody that inhibits VEGF function originally developed to treat cancers) for a FEVR patient, however, the role of anti-VEGF agents in FEVR amelioration remains unclear and has not been widely adopted. Despite current intervention options, loss of vision occurs in the majority of FEVR patients. The idea treatment for this condition would entail early detection with early intervention with a therapy that will prevent the complications from progressing altogether.